FINE FERROMAGNETIC POWDER FOR MAGNETIC RECORDING.

摘要

Improved fine ferromagnetic powder comprises platy ferrite crystal particles (1). (1) have a composition in which the molar ratio of Ba to Fe lies between 1/50 and 1/8 (preferred between 1/45 and 1/10) and in which the total amount of Ni and Zn per 1 mole of Fe lies between 0.07 and 0.5 mole (pref. 0.14-0.4 mole). The molecular ratio of Zn/Fe is 0.03 or more. The crystalline phase of (1) is magnetoplumbite, or spinel or a composite phase of these. The saturation magnetisation of (1) is 60 emu/g or more. (1) is produced by the following processes, a) an alkaline emulsion contg. Ba, Fe, Ni and Zn in the specified amounts and OH groups and having a pH of 11 or higher is heated at 30-250 C (pref. 60 - 200) deg.C to obtain a ferrite precursor, (b) the ferrite precursor is baked at 600-1000 deg. C to obtain platy ferrite crystalline particles which have a saturation magnetization of 60 emu/g or more. The OH group concn. in the emulsion is 1.5 mole/l or more.